Fig 1.
Typical data segments of AECG records.
(A) The beginning, extrema and end (from top to bottom) of a transient ST segment episode compatible with ischaemia. (B) Severe noise.
Fig 2.
The ECG of a normal heartbeat.
A heartbeat of a two-lead AECG record with marked points and intervals to estimate ST segment diagnostic and morphologic features.
Fig 3.
The ST segment KLT basis functions (they span over two ECG leads) obtained from the ESC DB.
The duration of the ST segment basis functions is 2 x 120 ms, from F + 40 ms to F + 160 ms, in 2 x 16 sample resolution.
Fig 4.
The derived LPT and KLT basis functions.
(A) The Legendre orthogonal polynomials as the ST segment basis functions, ΦL, spanning over a single ECG lead. (B) The ST segment KLT basis functions, ΦK, obtained from the LTST DB which span over a single ECG lead. The duration of the ST segment basis functions is 120 ms, from F + 40 ms to F + 160 ms, and are in 32 sample resolution.
Table 1.
Standard deviations of the coefficients of the KLT and LPT feature-vector time series.
Fig 5.
The trend plots of the derived diagnostic and morphologic feature-vector time series.
The second lead of record s20421 of the LTST DB from 04:00 [h:min] to 07:00 containing axis shifts and transient ischaemic ST segment episodes. From top to bottom: heart rate, h(j), in [bpm]; ST segment level, sl(2, j), and ST segment slope, ss(2, j), (resolution: 100μV/div); stream of human-expert annotated ischaemic ST segment episodes (long rectangles); and the first five KLT and the first five LPT ST segment coefficients, sK, k(2, j) and sL, k(2, j), with their corresponding Mahalanobis distance measures, dK(2, j) and dL(2, j), respectively, (resolution: 1ς/div). At the right: Heart beats according to markers A, B and C, prior to the axis shift [04:13:26.176], after the axis shift [04:43:30.416], and at the extrema of ischaemic ST episode [06:30:08.056] with marked interval (ST) where the KLT and LPT basis functions reside.
Fig 6.
ST segment episodes in terms of the KLT and LPT feature-vector time series representation.
(A) Example of ischaemic ST segment episode showing ST segment scooping (the first lead of record s30681, from 10:06 [h:min] to 10:36). (B) Example of non-ischaemic heart-rate related ST segment episode showing moving of the T wave closer to the QRS complex (the first lead of record s20431, from 00:30 to 01:00). Upper: The KLT feature-vector time series, sK(i, j). Middle: Human-expert annotated depressed ischaemic or elevated non-ischaemic ST segment episode. Lower: The LPT feature-vector time series, sL(i, j). Right: Normal reference heartbeat (dotted line) at the time marked with R with overlaid ischaemic or non-ischaemic heartbeat (solid line) at the extrema of the episode at the time marked with X.
Table 2.
Classification performance evaluation results.